Low-molecular weight homo- and copolymers of 1,3-dienes have been known for a long time. It is advantageous for many uses to alter the properties of the hydrophobic polymers in a controlled fashion by introduction of polar groups. One of these groups is the hydroxyl group because reactions with isocyanates, for example, can be carried out on such a group.
It is also known in the art that hydroxyl-terminated polybutadiene can provide polyurethanes having good hydrolytic stability, chemical resistance and a wide range of mechanical properties.
Processes for the preparation of polyhydroxybutadiene (hydroxyl-containing butadiene homopolymers) are known in the art, and may be prepared, for example, by the methods described in U.S. Pat. Nos. 3,055,952; 3,333,015; 3,338,861; 3,427,366; 3,673,168 and 3,796,762, incorporated herein by reference. For a review of polymeric butadienes see J. N. Henderson, Encyl. Polym. Sci. Eng. 1985, 2, 515-36 and W. Heitz, Telechelic Polymers: Synthesis and Applications, Chapter 4, p. 61 (1989).
In U.S. Pat. No. 4,460,801 there is disclosed a process for reacting butadiene and water in the presence of a palladium salt and boric acid in a polar, aprotic solvent to prepare an unsaturated fatty alcohol of the formula: ##STR1## where n=2 or 4.
U.S. Pat. No. 4,670,518 discloses a process for the production of low-molecular weight homo- and/or copolymers of 1,3-dienes carrying hydroxymethyl groups partially esterified with formic acid, comprising reacting 1,3-dienes having an average molecular weight of 500-8000 with formaldehyde at temperatures of 150.degree.-300.degree. C. optionally in the presence of a solvent and stabilizer.
Butadiene has been polymerized with four-valence molybdenum catalysts. See M. Zhao et al., C. A. Selects, p. 12 (19) 1986. In other work .alpha., .omega.-hydroxyl-terminated polybutadienes with different molecular weights and microstructures were prepared in nonpolar media using lithium-naphthalene-THF as a catalyst (See U.S. Pat. No. 3,055,952 and Germ. Pat. No. 1,173,658).
In U.S. Pat. No. 4,721,754 there is described a polybutadiene composition useful for the preparation of polyurea and/or polyurethane elastomers comprising a blend of a polyhydroxybutadiene homopolymer and an amine terminated polybutadiene.
A problem has existed in polybutadiene solvent recovery units wherein due to solids formation below the feed trays of the distillation columns, fouling may occur which plugs the trays and downcomers. The fouling is apparently caused by the presence of hydrogen peroxide, low molecular weight polybutadienes, polymeric precursors such as butadiene and vinylcyclohexene formed by the polymerization reaction. Such fouling may occur approximately every 5 to 6 days at high plant production rates thus requiring frequent and expensive shutdowns for cleaning.
U.S. Pat. No. 4,518,770 discloses a method of reducing the fouling in a distillation unit which comprises injecting into the distillation unit, along with the feed stream from which the polyhydroxybutadiene has been removed, an aqueous solution of an alkali metal sulfite or bisulfite.
It would be extremely desirable in the art if a process were available whereby low molecular weight oligomers could be prepared which possessed a high degree of OH functionality by a method which avoided the formation of solid or gel-type insoluble rubbers that are known to foul the reactor.